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I posted this question in the math forum on redddit, but it was deleted because it is not a math question.

I am hoping someone here can enlighten me.

In my life as an estimator for a machine tool builder, I have always used a learning curve model to estimate future repeat production.

That model is: Every time a quantity of parts is ran, the time to complete should improve; that improvement will be seen every time the quantity is doubled. In other words - with a 95% learning curve, a 5% improvement (100-95) will be seen between the first and second part, and again from the 2nd to the 4th, from the 4th to the 8th, etc. Every time the quantity doubles, the same percentage improvement is realized. (There is a little more to it, batch sizes and a 'forget factor' and so on, but I think you get the point.)

Every time a job is repeated, it is expected to go faster/cheaper because of experience and lessons learned.

If a job is able to be improved considerably every time it is re-ran, then the cost/time goes down considerably on subsequent runs. That is, a plot of cycle times or costs vs quantity, would show a very big drop from part 1 to part 2, from part 2 to part 4, from 4 to 8, etc. A big drop = a steep curve. Going down that curve happens quickly.

If a job is very difficult to improve upon, then the curve is considerably shallower, because the time to produce does not get better over time = shallow learning curve.

I have always used 'steep learning curve' to denote 'rapid improvement over time' but am now being told that is the opposite; apparently my definition is backward, and a SHALLOW learning curve means rapid improvement over time.

Could someone please set me straight on this?

I posted this question in the math forum on redddit, but it was deleted because it is not a math question. I am hoping someone here can enlighten me. In my life as an estimator for a machine tool builder, I have always used a learning curve model to estimate future repeat production. That model is: Every time a quantity of parts is ran, the time to complete should improve; that improvement will be seen every time the quantity is doubled. In other words - with a 95% learning curve, a 5% improvement (100-95) will be seen between the first and second part, and again from the 2nd to the 4th, from the 4th to the 8th, etc. Every time the quantity doubles, the same percentage improvement is realized. (There is a little more to it, batch sizes and a 'forget factor' and so on, but I think you get the point.) Every time a job is repeated, it is expected to go faster/cheaper because of experience and lessons learned. If a job is able to be improved considerably every time it is re-ran, then the cost/time goes down considerably on subsequent runs. That is, a plot of cycle times or costs vs quantity, would show a very big drop from part 1 to part 2, from part 2 to part 4, from 4 to 8, etc. A big drop = a steep curve. Going down that curve happens quickly. If a job is very difficult to improve upon, then the curve is considerably shallower, because the time to produce does not get better over time = shallow learning curve. I have always used 'steep learning curve' to denote 'rapid improvement over time' but am now being told that is the opposite; apparently my definition is backward, and a SHALLOW learning curve means rapid improvement over time. Could someone please set me straight on this?

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[–] [deleted] • 0 pt

Good stuff, but I usually also include a penalty based on batch sizes and time between runs... "Forget factor". Otherwise,this is exactly what I've used.

But "steep" in my usage has always meant "gets easier faster."

That seems to be the issue.

[–] [deleted] • 1 pt

It looks like TP Wright's Cost of Airplanes, PDF linked in my link, agrees with you. He even takes into account nonconsecutive orders or your forget factors.

I learned something new at least by reading through it.

[–] [deleted] • 1 pt

Me, too!

I took over estimating here about 10 years ago when the last guy retired. He explained the concept, but admitted he usually winged it.

I added it to a spreadsheet, gave it some realistic numbers, and never had an issue... Until I said "Software X has a pretty steep learning curve if you've used software Y, so you'll be fine."

Apparently people get hateful when you get that term wrong.